Double boiler



C. B. DEXTER DOUBLE BOILER Sept. 25, 1934.

Filed June 2, 1953 INVENTOR CARNOT B. DEXTER Patented Sept. 25, 1934 PATENT OFFICE UNITED STATES My invention relates to double boilers such as are in common use as kitchen utensils in households, and which comprise alower boiler which is customarily partly filled with water,

and an upper boiler which is set into the lower boiler and heated by the hot water or steam therein.

Such double boilers are ideal cooking vessels for many purposes, but they are subject to certain serious objections which arise from the fact that the water in the lower boiler may by oversight become evaporated, whereupon such lower vessel will be injured or destroyed and the food in the upper boiler spoiled. The use of such double boilers necessitates, therefore, constant attention on the part of the housewife to maintain'a safe amount of water in the lower boiler.

The chief object of my invention is to provide a means whereby a supplemental reservoir will supply water automatically to the lower boiler to keep a predetermined volume therein and so to overcome the objections and disadvantages above pointed out.

A further object of -my invention is to so design the lower boiler of a double boiler that it may be used with ,or without the supplemental water supply means, and when used without such means it will not change the normal functioning of the double boiler until the water is nearly boiled out when it will indicate such fact by a change in the point of escape of the steam.

A further object of my invention is to provide the lower. boiler with a. duct opening thereinto near, but spaced from, its bottom level and jopening externally thereof near itstop, whereby the duct will be sealed by the presence of the normalsupply of water in the lower boiler, but when said water becomes abnormally low steam will escape through said duct and give a signal calling for the refilling of the lower boiler.

A further object of my invention is to provide an auxiliary water supply reservoir, closed except for its discharge pipe which is adapted to be inserted into the duct in the lower boiler to a level where it will. be normally sealed when there is an ample supply of water in the lower boiler, but will be exposed when the water falls below a predetermined level, whereupon water will flow from such reservoir until said pipe is 50 a ain sealed and thusthe reservoir will act to maintain the water at such level in the lower boiler.

My invention further contemplates the provision of an auxiliary reservoir for use as an attachment for the double boiler, the reservoir preferably being annular to surround the upper boiler and seat on the lower boiler, and such reservoir may be provided with asbestos, or like heat insulation to prevent the water therein being brought to a boil and forcing the evacuation of its contents into the lower boiler faster than is needed to maintain the safety water level therein.

My invention further comprises the novel details of construction and arrangement of parts which in their preferred embodiments only are hereinafter more particularly described and claimed, reference being had to the accompany-' ing drawing which forms a part of this specification, and in which:

Fig. 1 is a side view of a double boiler adapted to have the water level therein maintained automatically from an external reservoir.

Fig. 2' is a similar view showing the auxiliary reservoir assembly onthe double boiler.

Fig; 3 is a detail view broken away of the lower boiler showing the preferred type' of water inlet duct.

.Fig. 4 is a detail view of the annular auxiliary reservoir inverted and shown being filled, the view being partly in section to show the insulation within the reservoir; and

Fig. 5 is a front view of a double boiler partly broken away and showing an auxiliary water supply tube leading from a detached reservoir not shown, through a modified type of water inlet duct in the lower boiler.

' Similar reference numerals refer to similar parts throughout the drawing.

In the embodiment of my invention illustrated, I show a conventional form of double boiler comprising a top 1 for the upper boiler 2, which has its reduced lower portion adapted to fit into the contracted upper portion of the lower boiler 3. I provide. an aperture 4 in the inwardly overhanging top lip of the lower boiler, and I mount in this aperture the upper end of a vertically depending duct or tube 5, which is made fast in any suitable manner and has a tight connection overhead With the marginal walls of the aperture 4 and at its lower end it is in communication with the lower boiler at what I term the safety water level therein. This communication maybe established through a side port 6 in the duct 5 or, as is shown in Fig. 5, the duct 11 may terminate at such safety level.

I have shown the supplemental water reservoir adapted to be mounted as an attachment on the double boiler, but it is to be understood that it does not necessarily have to be mounted upon the double boiler, but may be supported in any convenient manner adjacent to the intended point of use of the double boiler and at a level substantially above the level of water which it is intended respond to that in the lower boiler.

on the inside wall lined with asbestos 12, or other suitable heat insulating lining, though this is not essential as it is of value only when the double boiler is liable to be carelessly subjected to excessive heat.

This reservoir 7 is entirely closed air tight except for its water discharge pipe 8 which opens through its bottom and is adapted to telescope loosely into the duct when the reservoir is seated in operating position on the double boiler, as

.shown in Fig. 2. The pipe 8, under such conditions,'extends down to what I term the predetermined level at which it is desired to maintain the water in the lower boiler, which is above the safety level that is fixed at the port 6 or the lower open end of tube 11.

In Fig. 4 I show how this reservoir .7 can be readily filled, its pipe 8 being amply large for the free inflow of water from a faucet and the corresponding escape of air therefrom while it is being filled. However, when this reservoir is inverted and its pipe 8 telescoped into the duct 5,

it will leave a suflicient clearance for the inflow ofreplacement air between it and the duct 5. When this reservoir is mounted on the lower boiler, the upper boiler can be readily set in position and removed without disturbing the reservoir.

Assuming the parts assembled as shown in Fig. 2, the operation of my invention will be readily understood by those skilled in this art, and its advantages appreciated. The supplemental body of water carried in the air tight reservoir '7 will be held in check therein so long as the lower end of its outlet pipe 8 is submerged in and sealed by the water standing in tube 5 in the lower boiler and the water level in this tube will always cor- I As soon as the water falls to a predetermined level in the lower .boiler, the lower end of the outlet pipe 8 will be exposed and thereupon the seal will 'be broken and the reservoir will be free to discharge its contents through pipe 8 and tube 5 into boiler 3 until its water level has been restored and again seals pipe 8, and this process continues so long as there is water in the supplemental reservoir '7.

In practice, an ample volume of water, approximately equal to that with which the lower boiler is customarily filled, can be carried in this supplemental reservoir 7, and when it is in use it will be at once obvious that long cooking operations can be carried out in the double boiler without requiring attention or frequent water replacement, thereby releasing the housewife from watching the double boiler when in use and leaving her free to attend to other duties. .The double volume of water thus provided being ample for any ordinary cooking operation, the danger of injuring or burning up the lower boiler is practically eliminated.

It is to beunderstood that the supplemental reservoir can have any desired size or shape and that its outlet pipe may be rigid as in Fig. 4 or flexible as the duct 13 (Fig. 5), and that it may be mounted on, or independently supported adjacent to, the double boiler with its duct 13 leading therefrom to the desired level in the tube 8 in the lower boiler. Where, due to careless use the supplemental reservoir may be exposed to high temperature, its bottom and inside wall may be lined with a refractory material 12, such as asbestos, which will prevent the tendency of the water in this reservoir to be brought readily to a boil, thus causing premature flow of water from the reservoir into the lower. boiler.

While I have shown my invention in but two forms, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various other changes and modifications, without departing from the spirit thereof, and I desire, therefore, that only such limitations shall be placed thereupon as are imposed by the prior art or as are specifically set forth in the appended claims.

What I claim is:-'

1. The combination with a double boiler having upper and lower boilers, of an auxiliary water reservoir closed air tight except for an outlet duct which opens into the. lower boiler in position to be-sealed by a predetermined volume of water therein.

2. A double boiler having in its lower boiler a duct-communicating therewith at a point below normal water level and opening externally thereof above said level, and an auxiliary water supply reservoir closed except for an outlet conduit which conduit telescopes into said duct into position to be sealed by water standing therein.

3. In a double boiler, a lower boiler having a tube opening thereinto below its normal water level and opening externally above said level, and an auxiliary water reservoir adapted to be mounted on the double boiler and closed air tight except for an outlet pipe which is adapted to enter said tube and to be sealed by a predetermined water level therein.

4.- The combination with a double boiler having in its lower boiler a vertical tube that opens above without said boiler and opens below within the lower boiler near a predetermined water level to be maintained therein, and an auxiliary water reservoir closed tight except for an .outlet pipe which is ,adapted to depend into said tube to said predetermined water level when the reservoir is mounted onthe double boiler.

5. In a double boile in combination, an upper boiler, a lower boiler having a tube opening below within the lower boiler and opening above through the top portion of said lower boiler, an

annular water reservoir adapted to surround the upper boiler and to be seated on the lower boiler, said reservoir being sealed air tight except for a bottom outlet pipe adapted to depend through surround the upper boiler and sealed air tight except for a water. discharge pipe which depends low enough to approach the bottom level of the lower boiler when the water chamber is seated thereon.

7. An auxiliary reservoir according to. claim 6, in which the walls of said water chamber most exposed to heat are heat insulated.

8. In a double boiler, in combination, a lower boiler having an inwardly overhung top lip and a tube opening vertically therethrough and at its: lower end communicating with said lower boiler at the safety level for water to be maintained therein, an upper boiler adapted to telescope into the lower boiler, and an annular water reservoir adapted to seat on said top lip and sealed air tight except for a bottom water outlet pipe which telescopes loosely into said tube and terminates at the predetermined level of water desirable to be maintained automatically in the lower boiler. CARNOT BELLINGER DEXTER. 

